The present invention relates to the general field of the cooling of gas turbine blades, in particular the movable blades of a turbine engine gas turbine.
The gas turbine blades of a turbine engine, such as the movable blades of the high-pressure turbine for example, are subjected to the very high temperatures of the gases coming from the combustion chamber. These temperatures reach values considerably higher than those that the blades of the turbine can withstand without damage, the result of which is to limit their service life.
To remedy this problem, providing these blades with internal cooling circuits is well known. By virtue of such cooling circuits, air, which is generally introduced into the blade via its base, passes through it following a route formed by cavities made in the blade before being ejected via apertures opening at the surface of the blade.
There are many different implementations of these cooling circuits. Thus, some circuits use cooling cavities that occupy the entire width of the blade (that is to say extend from the concave side to the convex side of the blade). Other circuits propose the use of edge cooling cavities occupying only a single side of the blade (concave side or convex side) or both sides with the addition of a large central cavity between these edge cavities.
In terms of mechanical strength, a gas turbine blade exhibits a good service life if its concave side and convex side faces have neighboring temperatures (that is to say if the thermal gradient between these faces is small). Furthermore, irrespective of the method of implementing the cooling circuits, the internal cooling of a turbine blade is provided by internal convection of a flow of fresh air over the walls of the cavities forming these circuits. The result of this is a different heat exchange on each wall of the cavity, independently of whether this is smooth or disrupted or whether the blade is fixed or movable.
However, the heat exchange with the hot gases circulating outside the blade is greater on the concave side than on the convex side of the blade. Consequently, in order to compensate for this phenomenon and thus obtain a small thermal gradient between the concave side and convex side faces of the blade, it is necessary to greatly cool the internal walls of the cavities of the cooling circuit which are disposed on the concave side of the blade.
For a movable gas turbine blade, when the flow of air in the cavities of the cooling circuit is centrifugal, and despite the effects of the Coriolis force which increase the heat exchanges internal to the concave side of the blade, the difference with the heat exchanges taking place at the convex side of the blade remains too great to obtain a small thermal gradient. Similarly, when the flow of air in the cavities of the cooling circuit of the movable blade is centripetal, the heat exchange naturally favors the convex side of the blade, which further increases the temperature difference between the concave side and convex side faces of the blade.